He has 30 altogether. But they are all at Professor's Lab and he has only used one of the thirty for battle.
> Ash spent some time in the Safari Zone in the episode EP035. He was
> attempting to catch as many Pokémon as possible, though all he ended
> up with were thirty Tauros as they always ran in front of his Safari
> Balls when he tried to make a catch. At the end of Ash's adventures in
> the Safari Zone, all thirty Tauros were sent to Professor Oak's
Bulbapedia's page has all you need to know about this.